Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $199.95   11.616%   $223.1762   $223.18   $223.20   $223.20  
  Purchase #2 $203.79   6.329%   $216.6879   $216.69   $216.70   $216.70  
  Purchase #3 $12.98   13.284%   $14.7043   $14.70   $14.70   $14.70  
  Purchase #4 $56.89   12.284%   $63.8784   $63.88   $63.90   $63.90  
  Purchase #5 $221.69   12.633%   $249.6961   $249.70   $249.70   $249.70  
  Purchase #6 $217.65   11.607%   $242.9126   $242.91   $242.90   $242.90  
  Purchase #7 $142.62   13.475%   $161.838   $161.84   $161.85   $161.80  
  7 purchase totals = $1,055.57       $1,172.8935   $1,172.90   $1,172.95   $1,172.90